Polyamide ligand-containing polymeric resins and methods of using the same for removing, separating and/or concentrating desired metal ions from solutions

ABSTRACT

The present invention is drawn to polyamide ligand-containing polymeric resins and methods of using the same for removing, separating, and/or concentrating certain desired metal ions from solutions, even when the desired ions are in the presence of other metal ions and/or hydrogen ions at much higher concentrations. The unique composition of matter of this invention is a polyamide ligand-containing polymeric resin which is a reaction product of a hydroxymethylated polyamide ligand and a polymerization and/or crosslinking agent. Specifically, the polymeric resins of the present invention are comprised of from 10 to 50,000 polyamide ligand units wherein each polyamide ligand unit contains at least three amide groups (preferably from three to eight amide groups) and two amine groups separated by at least two carbons. Each amide group, after polymerization, may remain hydroxymethylated or be crosslinked to other polyamide ligand units through a crosslinking agent.

PRIOR APPLICATION

This is a division of application Ser. No. 09/444,114 filed Nov. 22,1999 now U.S. Pat. No. 6,335,420.

FIELD OF THE INVENTION

The present invention relates to polyamide ligand-containing polymericresins which are polymerized and/or crosslinked and methods of using thesame for removing, separating, and/or concentrating certain desiredmetal ions from solutions, even when the desired ions are in thepresence of other metal ions and/or hydrogen ions at much higherconcentrations.

BACKGROUND OF THE INVENTION

Effective methods for the separation and recovery of particular ionssuch as the transition, post-transition, and alkaline earth metal ionsfrom solution mixtures containing these and other metal ions are ofgreat importance in modern technology. Particularly, it is difficult toseparate and recover certain metal ions such as Cd²⁺, Pb²⁺, Ag⁺, Ni²⁺,Co²⁺, Fe³⁺, Cu²⁺, Sr²⁺, and/or Ca²⁺ from the presence of even moderateamounts of hydrogen ion (H⁺). It is also very difficult to remove thesedesired metal ions when present at low concentrations in solutions thatcontain other, non-desired metal ions at much greater concentrations.Thus, there is a real need for a composition of matter and an associatedmethod that may be used for selectively separating certain transition,post-transition, and alkaline earth metal ions from other non-desirableions.

It is known that ethylenediaminetetraacetamide (EDTAA),diethylenetriaminepentaacetamide (DTPAA), and nitrilotriacetamide (NTAA)form strong complexes with various metal ions in solution. Thesemolecules may be shown as Formulas 1-3 respectively below:

J. M. Grana-Molares, C. Baluja-Santos, A. Alvarez-Devesa and F.Bermejo-Martinez, Etude Spectrophotometrigue des Complexes duCobalt(III) avec les Amides de l'EDTA et du DTPA, Analysis, Volume 7,249-252 (1979) reported on the synthesis of EDTAA and DTPAA and theirability to complex Co(III) as shown by a spectrophotometric technique.In a different study, L. Przyborowski, Complex Compounds of Amides andThioamides of Aminopolycarboxylic Acids, Part III. Synthesis, Propertiesand Copper(II) Complexes of Nitrilotriacetotriamide andEthylenediaminetetraacetotetraamide, Roczniki Chemii, Volume 44,1883-1893 (1970) showed that NTAA and EDTAA could be prepared bymodifying known methods and that Cu(II) formed strong complexes withNTAA.

More recently, a great deal of research has been done in the synthesisand metal ion complexation properties of polyamide-containing azacrownethers such as those containing acetamide, propionamide, and peptideside arms. R. Kataky, K. E. Matthes, P. E. Nicholson, D. Parker and H-J.Buschmann, Synthesis and Binding Properties of Amide-FunctionalizedPolyazamacrocycles, Journal of the Chemical Society, Perkin Transactions2, 1425-1432 (1990) reported on the synthesis and complexationproperties of per-N-(dimethylacetamido)-substituted triaza-9-crown-3,aza-12-crown-4, diaza-12-crown-4, and tetraaza-12-crown-4. The ligatingagents 1,4,7,10-tetrakis(N,N-dimethylacetamido)-1,4,7,10-tetraazacyclododecane and1,7-dioxo-4,10-bis(N,N-dimethylacetamido)-4,10-diazacyclododecane aretwo chemical structures that were synthesized and which arerepresentative of polyamide-containing ligating agents of the presentinvention. These ligating agents are shown respectively below inFormulas 4 and 5:

The diamide of Formula 5 was shown to form complexes with all of thealkali metal and alkaline earth metal cations. Further, this diamide wasshown to have significant selectivity for Ca²⁺ over the other cationsstudied. However, a diamide similar to that of Formula 5, but containingone more methylene group in each amide-containing arm (thus, having twoN,N-dimethylpropioamido substituents), was shown to form weakercomplexes with these same metal ions.

Further studies of amide ligands, such as those depicted by formulas 4and 5, have concluded that the size of the metal ion-ligand chelate ringdetermines the strength of the interaction between the ligand and themetal ions. For example, a five-membered ring favored the smallercations over a six-membered ring. Representative of fully chelatedmetals (Me) having five- and six-membered amide rings attached are shownin Formulas 6 and 7 respectively below:

H. Maumela, R. D. Hancock, L. Carlton, and J. H. Reibenspies and K. P.Wainwright, The Amide Oxygen as a Donor Group. Metal Ion ComplexingProperties of Tetra-N-Acetamide Substituted Cyclen: A Crystallographic,NMR, Molecular Mechanics and Thermodynamic Study, Journal of theAmerican Chemical Society, Volume 117, 6698-707 (1995), reported thesynthesis of 1,4,7,10-tetraazacyclododecane (DOTAM) which is theunsubstituted amide analogue of the tetraamide of Formula 4. DOTAM iscapable of forming complexes with a host of metal ions including manytransition and post-transition metal ions. DOTAM also forms strongcomplexes with Cd²⁺ and Pb²⁺, even at pH levels of as low as 0.3 whichis equivalent to a hydrogen ion concentration of 0.5 Molar. DOTAM may berepresented by Formula 8 below:

The articles cited above disclose procedures for synthesizing anddemonstrating limited useful complexation properties ofpolyamide-containing ligand molecules. However, researchers have notpreviously been able to incorporate polyamide-containing ligands intosolid phase separation systems. This is significant because thesepolyamide-containing ligands merely act as a solute in solution bycomplexing with selected ions, but provide no effective means for ionseparation.

The use of polymeric resins for selective removal of ions is not a newconcept of itself. In U.S. Pat. No. 5,656,702, the use ofpoly(hydroxyarylene) polymeric resins is disclosed for removing alkalimetals, particularly cesium, from industrial streams. However, neverbefore have polyamide ligand-containing polymeric resins beensuccessfully synthesized that can be used in a solid phase separationsystem to concentrate and remove desired metal ions such as membersselected from the group consisting of Cd²⁺, Pb²⁺, Ag⁺, Ni²⁺, Co²⁺, Fe³⁺,Cu²⁺, Sr²⁺, an Ca²⁺ from source solutions.

SUMMARY OF THE INVENTION

The present invention is drawn to polyamide ligand-containing polymericresins and methods of using the same for removing, separating, and/orconcentrating certain desired divalent metal ions including transition,post-transition, and alkaline earth metal ions from source solutions.The unique composition of matter of this invention is a polyamideligand-containing polymeric resin which has been polymerized and/orcrosslinked. These resins are generally a reaction product of ahydroxymethylated polyamide ligand and a polymerization and/orcrosslinking agent. Specifically, the polymeric resins of the presentinvention are comprised of from 10 to 50,000 polyamide ligand unitswherein each polyamide ligand unit is defined by three or more amidegroups, preferably from three to eight amide groups, and two or moreamine nitrogen donor atoms separated by at least two carbons.

The present invention is particularly useful for the removing of ionsselected from the group consisting of Cd²⁺, Pb²⁺, Ag⁺, Ni²⁺, Co²⁺, Fe³⁺,Cu²⁺, Sr²⁺, Ca²⁺, and combinations thereof from source solutions. Thisis true whether the desired ions are present at very low or very highconcentrations, i.e., from ppb to g/l.

The concentration of desired ions is accomplished by forming a complexof desired ions with the polyamide ligand-containing polymeric resins byflowing a source solution containing the desired ions through a columnpacked with the polymeric resin beads or granules. The metal ion and thepolyamide ligand-containing polymeric resins are then decoupled byflowing a receiving liquid through the column (in much smaller volumethan the volume of source solution passed through the column) toremoving, separating, and/or concentrating the desired ions in thereceiving liquid solution. The receiving liquid or recovery solutionforms a stronger complex with the desired ions than does the polyamideligand-containing polymeric resins, or alternatively, temporarily formsa stronger interaction with the polyamide ligand-containing polymericresins than does the desired metal ions. In either case, the desiredmetal ions are quantitatively stripped from the polyamideligand-containing polymeric resins in a concentrated form in thereceiving solution. The recovery of desired ions from the receivingliquid may be accomplished by various methods commonly known in the artincluding evaporation, electrowinning, and precipitation among others.

DETAILED DESCRIPTION OF THE INVENTION

The polyamide ligand-containing polymeric resins of the presentinvention are a reaction product of a polyamide ligand and formaldehydeor other suitable compound capable of forming a hydroxymethylatedpolyamide ligand. The hydroxymethylated polyamide ligand is thenpolymerized using a polymerization and/or crosslinking agent to form thepolyamide ligand-containing polymeric resins. The polyamideligand-containing polymeric resins of the present invention arecomprised of from 10 to 50,000 polyamide ligand units wherein eachpolyamide ligand unit or monomer is defined by three or more amidegroups, preferably from three to eight amide groups, as well as two ormore amine nitrogen donor atoms separated by at least two carbons. Eachamide group of the polyamide ligand unit, after hydroxymethylation, mayremain hydroxymethylated or be polymerized and/or crosslinked to otherpolyamide ligand units through a polymerization agent or a crosslinkingagent. At least one of the amide groups of the resin must be polymerizedor crosslinked, preferably from two to eight.

The structure of the present invention may be represented generally byFormula 9 as follows:

(LX_(m))_(n)  Formula 9

wherein L represents the polyamide-containing ligand having three ormore amide groups, preferably from three to eight amide groups, and twoor more amine nitrogens separated by at least two carbons, n may be aninteger from about 10 to 50,000, m is at least three, preferably fromthree to eight, and X may be CH₂OH, CH₂O—, CH₂—, a crosslinking agent,or a resulting group from polymerization with the proviso that each Xgroup is bonded individually to L and at least one X group per polyamideligand unit is involved in the polymerization or crosslinking.

Amide groups of the ligand which remain hydroxymethylated afterpolymerization are free to bind with the desired metal ions according tothe present invention. However, the amide groups of the ligand which areinvolved in the polymerization reaction or crosslinking may also beinvolved in the binding of the desired metal ions. In other words, it isnot the purpose of the invention to describe specifically how each ofthe polymeric resins complex with each specific desired ion, only thatthe polymeric resins described herein will bind with the desired ionsalso described herein.

It is to be noted that the crosslinking agents or polymerization agentsthat may be used and the processes of crosslinking and/or polymerizationare known in the art. For example, phenols, resorcinol, fluoroglucinol,aromatic or aliphatic amines, pyrroles, indoles, nitrates, esters,ketones, and nitriles, and/or other known crosslinking agents may beused. Further, polymerization agents that may be used includebisaldehydes, polyaldehydes, dihalogens, polyhalogens, dihalogens ofdiacids, polyhalogens of polyacids, diesters, polyesters, anhydrides ofacids, diepoxides, polyepoxides, and/or other known polymerizationagents.

In one preferred embodiment, a hydroxymethylated polyamide ligand may bepolymerized linearly using a polymerization agent. In a second preferredembodiment, the generally linear polymer described above may becrosslinked using a crosslinking agent. In another preferred embodiment,a hydroxymethylated polyamide ligand may be both polymerized andcrosslinked using only a single polymerization/crosslinking agent. Assuch, one skilled in the art may utilize these known polymerizationagents and crosslinking agents in any functional combination and notdepart from the scope of the present invention.

Representative examples of polyamide ligands (L) that may behydroxymethylated and then polymerized to form polyamideligand-containing polymeric resins that have at least three amide groupsand two or more amine nitrogens separated by at least two carbonsinclude: ethylenebis(oxyethylenenitrilo) tetraacetic acid (EGTAM),diaza-18-crown-6-tetraamide,ethylenediaminetetraacetamide-N-methylenepropanetetraamine (EDTAAMT),tris(2-aminoethyl)amine pentaamide (TRENPAM), anddiethylenetriaminepentaacetamide (DTPAM). This list is intended only tobe representative of the possible ligands that may be used, the limitingfactor being the presence of at least three amide groups, preferablyfrom three to eight amide groups, and at least two amine nitrogensseparated by two or more carbons. Further variations of these ligandsmay also be used. For example, tris(2-aminoethyl)amine pentaamide(TRENPAM) may be alkyl or aryl substituted. Once polymerized, thepolyamide-ligand units of the present invention form beads and/orgranules which may be used for ion removal, separation, and/orconcentration.

As summarized above, the present invention is drawn to a novelcomposition of matter comprising polyamide ligand-containing polymericresins. The present invention is also Undrawn to methods for thepreferential removal, separation, and/or concentration of certaindesired metal ions, such as certain transition, post-transition, andalkaline earth metal ions from solution. The solution from which thedesired ions may be removed may contain other metal ions or hydrogenions present at greater concentrations than the desired ions. Forexample, Cd²⁺, Pb²⁺, and Ag⁺ may be removed from acidic and or highlychelative matrices and Ni²⁺, Co²⁺, Fe³⁺, Cu²⁺, Sr²⁺, and Ca²⁺ may beremoved from slightly acidic to neutral pH matrices and from chelatingmatrices. Moreover, the above described polyamide ligand-containingpolymeric resins provide a mechanism for separating ppb to ppm levels ofCd²⁺ and Pb²⁺ from concentrated acid solution by using separationtechniques and equipment generally known in the art.

The method for separating and recovering desired ions is accomplished byforming a complex of the desired ions with polyamide ligand-containingpolymeric resins. Specifically, this is accomplished by flowing a sourcesolution containing the desired ion(s) through a packed column or otherknown device with these polymeric resin beads or granules in order tocomplex or chelate the desired metal ion(s) to one or more polyamideligand units of the polyamide ligand-containing polymeric resins.Subsequently, the desired cation which is bound to the polyamideligand-containing polymeric resins is released by flowing acomplex-breaking receiving liquid in much smaller volume than the volumeof source solution originally passed through the column or other knowndevice. This removes, separates and/or concentrates the desired ions inthe receiving liquid solution by either (a) forming a stronger complexwith the desired transition, post-transition, or alkaline earth metalion(s) than do the polymeric resins, or (b) temporarily forming astronger interaction with the polymeric resins than do the desired metalion(s), and thus, the desired metal ion(s) are quantitatively strippedfrom the polyamide ligand-containing polymeric resins in concentratedform in the receiving solution. The recovery of desired metal ion(s)from the receiving liquid is accomplished by evaporation,electrowinning, precipitation or by other known methods.

EXAMPLES

The following examples should not be considered as limitations of thepresent invention, but are merely intended to teach how to make thepolyamide ligand-containing polymeric resins based upon currentexperimental data.

Example 1 Synthesis of Ethylenediaminetetraacetamide (EDTAM) andPolymerization Forming a Polymeric Resin

Step 1—About 140 g (0.48 mole) of ethylenediaminetetraacetic acid (EDTA)(A) and 600 mL of ethyl alcohol were placed in a flask equipped with aSoxhlet extraction apparatus and refluxed while HCl gas was continuouslybubbled through the system. After the mixture became homogeneous, it wasrefluxed for another 5 hours. The ethanol was then removed byevaporation. A 10% sodium carbonate aqueous solution was added to adjustthe pH of the solution to about 8. The solution was then extracted withdiethyl ether. The diethyl ether organic layer was separated, dried byadding sodium sulfate and concentrated under reduced pressure. About 153g (79% of theoretical) of the tetraester (B) was obtained afterpurification by column chromatography (silica, ethyl acetate). Puritywas determined by NMR giving the following values: ¹H NMR (300 MHz,DCCl₃, [deuteriochloroform]) δ4.2 (q, 8H), 3.6 (s, 8H), 2.9 (s4H), 1.3(t, 12H); FABMS 404 (M⁺)

Step 2—About 10 g (25 mmole) of tetraester (B) was dissolved in 30 mL ofmethyl alcohol and combined with 200 mL of 7N ammonia solution in methylalcohol. The mixture was stirred for 5 days at room temperature. A whiteprecipitate formed that was filtered and washed with methyl alcohol. Theprecipitate was then dried in a vacuum oven. About 5 g of EDTAA (C) wasformed.

Step 3—About 5 g of EDTAA (C), was dissolved in 100 mL of water andcombined with a solution containing 2 g of paraformaldehyde in 8 mL ofwater. The system was stirred at room temperature for 3 hours. The waterwas then evaporated and the hydroxymethylated tetraacetamide residue wasdried under a vacuum using phosphorous pentaoxide.

Step 4—About 2 g of the hydroxymethylated tetraacetamide obtained inStep 3 was treated with 10 mL of methanesulfonic acid at roomtemperature for 2 hours. A polymeric mass (D) was formed which wasfiltered, washed with water and dried under a vacuum at 50° C. usingphosphorous pentaoxide. About 2 g of the EDTAM polymeric resin (D) wasobtained.

The EDTAM polymeric resin structure (D) illustrates an essentiallylinear polymeric resin. However, this structure may be furtherpolymerized or crosslinked using additional amounts of thepolymerization agent, an additional polymerization agent, or acrosslinking agent. The structure of such a crosslinked resin structurewould be difficult to ascertain as it would depend on the crosslinkingagent, the number of amide groups entering into the crosslinkingreaction, the degree of polymerization, and other variables known bythose skilled in the art.

Example 2 Synthesis of Diethylenetriaminepentaacetamide (DTPAM) andPolymerization Forming a Crosslinked Polymeric Resin

Step 1—About 189 g (0.48 moles) of tris(2-aminoethyl) pentaacetic acid(A) and 1000 mL of ethyl alcohol were placed in a flask equipped with aSoxhlet extraction apparatus and refluxed while HCl gas was continuouslybubbled through the system. After the mixture became homogeneous, it wasrefluxed for another 7 hours. The ethanol was then removed byevaporation. A 10% sodium carbonate aqueous solution was added to adjustthe pH of the solution to about 8. The solution was then extracted withdiethyl ether. The diethyl ether organic layer was separated, dried byadding sodium sulfate and concentrated under reduced pressure. About 192g (75% of theoretical) of the pentaester (B), was obtained afterpurification by column chromatography (silica, ethyl acetate).

Purity was determined by NMR giving the following values: ¹H NMR (300MHz, DCCl₃, [deuteriochloroform]) δ4.2 (q, 10H), 3.6 (mm, 10H), 3.2 (m,4H), 3.0 (m, 4H), 1.3 (t, 15H), FABMS 537 (M⁺).

Step 2—About 13 g (25 mmole) of the pentaester (B) was dissolved in 40mL of methyl alcohol and combined with 200 mL of 7N ammonia solution inmethyl alcohol. The mixture was stirred for 6 days at room temperature.A white precipitate formed that was filtered and washed with methylalcohol. The precipitate was then dried in a vacuum oven. About 6 g ofDTPAA (C) was formed.

Step 3—The hydroxymethylated pentaacetamide derivative of DTPAA wasprepared by dissolving DTPAA (C) in water and combining with an aqueoussolution of paraformaldehyde. The system was stirred for 3 hours at roomtemperature.

Step 4—About 3 g (5.7 mmole) of cadmium nitrate tetrahydrate wasdissolved in 50 mL of water and added to the hydroxymethylated compoundsolution of Step 3. A cadmium complex was allowed to form by stirringthe complex for 20 minutes at room temperature. The complex was used asa template for polymerization. About 1.5 g of fluoroglucinol in 20 mL ofethyl alcohol and 2 mL of concentrated hydrochloric acid were added tothe solution. The solution was kept at a temperature of 60° C. for 3hours then stirred at room temperature overnight. A polymeric resin (D)formed which was filtered, washed with water then methanol and driedunder a vacuum at 50° C. using phosphorous pentaoxide. About 4.1 g ofthe DTPAM polymeric resin (D) was obtained.

In the present example, paraformaldehyde is used to prepare thehydroxymethylated pentaacetamide derivative of DTPAA. If used in excess,the paraformaldehyde may initiate some polymerization. However, in thepresent example, the bulk of the polymerization and/or crosslinking is aresult of the addition of the fluoroglucinol. Therefore, in Formula D ofthis example, R may represents either a hydroxymethyl group, i.e.,CH₂OH, a resulting group from any polymerization that occurs, or thefollowing crosslinking agent which is a derived from fluoroglucinol:

where R′ is either an —OH group or another polyamide ligand unit on thepolymer itself, i.e., crosslinking. If both of the R′ variables are —OH,then there is no crosslinking. Therefore, it is preferably that at leastone R′ group is involved in crosslinking, i.e., not an —OH group.Further, at least one of the R groups of Formula D must be involved inthe polymerization or crosslinking, preferably from two to five.

Example 3 Separations Using the DTPAM Polymeric Resin of Example 2

In this example, 0.1 g of the DTPAM polymer of Example 2 was placed in apacked column. A 75 mL source solution containing 2 ppm (parts permillion) of Sr²⁺ in 0.05 M KCl, 0.1 M sodium acetate, and 0.01 M aceticacid was passed through the column. About 2 mL of water was then passedthrough the column to wash out the remaining loading solution. Next, theSr²⁺ was eluted with 1 mL of 0.5 M H₂SO₄. Analysis of the abovesolutions by Atomic Adsorption Spectroscopy (AA) showed that greaterthan 99% of the Sr²⁺ originally present in the source solution.described above was separated into the 1 mL receiving solution.Furthermore, the K⁺ and Na⁺ levels in the receiving liquid were lessthan 1 ppm.

We claim:
 1. A method for removing, separating, or concentratingselected ions from a source solution comprising the steps of: (a)contacting said source solution with a polyamide ligand-containingpolymeric resin which is a reaction product of a hydroxymethylatedpolyamide ligand and one or more agents selected from the groupconsisting of polymerization agents, and crosslinking agents, saidpolymeric resin being comprised of from 10 to 50,000 polyamide ligandunits, and wherein said polymeric resin has an affinity for saidselected ions such as to form a complex between said selected ions andsaid polymeric resin; (b) removing the source solution from contact withsaid polymeric resin to which said selected ions have been complexed;and (c) contacting said polymeric resin having said selected ionscomplexed thereto with a smaller volume of an aqueous receiving solutionin which said selected ions are either soluble, or which has greateraffinity for such selected ions than does the polymeric resin, therebyquantitatively stripping such selected ions from the ligand andrecovering said selected ions in concentrated form in said receivingsolution.
 2. A method according to claim 1 wherein each of saidpolyamide ligand units has three or more amide groups and two or moreamine nitrogens separated by at least two carbons.
 3. A method accordingto claim 2 wherein each of said polyamide ligand units has from three toeight amide groups.
 4. A method according to claim 3 wherein at leastone amide group of said polyamide ligand unit is polymerized orcrosslinked to another polyamide ligand unit by a polymerization agentor a crosslinking agent.
 5. A method according to claim 4 wherein fromtwo to eight amide groups of said polyamide ligand unit are polymerizedor crosslinked to one or more polyamide ligand unit by a polymerizationagent or a crosslinking agent.
 6. A method according to claim 4 whereinsaid polymerization agent is selected from the group consisting ofpolyaldehydes, polyhalogens, polyhalogens of polyacids, polyesters,anhydrides of acids, polyepoxides, and combinations thereof.
 7. A methodaccording to claim 4 wherein said crosslinking agent is selected fromthe group consisting of phenols, resorcinols, fluoroglucinols, aromaticamines, aliphatic amines, pyrroles, indoles, nitrates, esters, ketones,nitriles, and combinations thereof.
 8. A method according to claim 4wherein said hydroxymethylated polyamide ligand is derived from a memberselected from the group consisting of ethylenebis(oxyethylenenitrilo)tetraacetic acid (EGTAM),diaza-18-crown-6-tetraamide,ethylenediaminetetraacetamide-N-methylenepropanetetraamine (EDTAAMT),tris(2-aminoethyl)amine pentaamide (TRENPAM),diethylenetriaminepentaacetamide (DTPAM), and combinations thereof.
 9. Amethod according to claim 8 wherein said hydroxymethylated polyamideligand is derived from ethylene bis(oxyethylenenitrilo)tetraacetic acid(EGTAM).
 10. A method according to claim 8 wherein saidhydroxymethylated polyamide ligand is derived fromdiaza-18-crown-6-tetraamide.
 11. A method according to claim 8 whereinsaid hydroxymethylated polyamide ligand is derived fromethylenediaminetetraacetamide-N-methylenepropanetetraamine (EDTAAMT).12. A method according to claim 8 wherein said hydroxymethylatedpolyamide ligand is derived from tris(2-aminoethyl)amine pentaamide(TRENPAM).
 13. A method according to claim 8 wherein saidhydroxymethylated polyamide ligand is derived fromdiethylenetriaminepentaacetamide (DTPAM).
 14. A method according toclaim 4 wherein said selected ion is a member selected from the groupconsisting of transition ions, post-transition ions, alkaline earthmetal ions, and combinations thereof.
 15. A method according to claim 14wherein said selected ion is one or more transition metal ions.
 16. Amethod according to claim 15 wherein said transition metal ion isselected from the group consisting of Cd²⁺, Ag⁺, Ni²⁺, Co²⁺, Fe³⁺, Cu²⁺,Sr²⁺, Ca²⁺, and combinations thereof.
 17. A method according to claim 16wherein said transition metal ion is Cd²⁺.
 18. A method according toclaim 14 wherein said selected ion is one or more post-transition metalions.
 19. A method according to claim 18 wherein said post-transitionmetal ion is Pb²⁺.
 20. A method according to claim 14 wherein saidselected ion is one or more alkaline earth metal ions.
 21. A methodaccording to claim 20 wherein said alkaline earth metal ion is selectedfrom the group consisting of Ca²⁺, Sr²⁺, and combinations thereof.